This invention relates to a method and apparatus for the preparation of a liquid sample for quantitative determination of boron. More particularly, this invention relates to a method and apparatus for the preparation of a liquid sample for quantitative determination of boron wherein the boron is converted to the trimethyl borate ester which is immediately withdrawn in the gaseous state for quantitative determination by flame photometry.
Boron is used in many ways in industrial processes, including various stages of the production of nuclear energy from fissile materials. It is frequently necessary to analyze industrial products and byproducts for their boron content. A variety of methods have been developed for both the qualitative and quantitative determination of boron including gravimetry, titration, electrochemistry and photometry. Photometric and spectrophotometric methods in particular have been developed because of their ease of performance, accuracy, and reliability.
Flame photometry has been extensively applied to boron analysis. The sample of interest is introduced into a flame in a controlled manner, whereupon the boron in the sample is oxidized to BO.sub.2, which in turn is excited to emit a characteristic spectrum, the intensity of which is a function of the quantity of boron present in the flame. In the last 30 years flame photometry has been used on many different types of boron-containing samples with varying degrees of success. A comprehensive review of this work is given in Analytical Flame Spectroscopy, Ch. 5, "Nonmetals" by Paul T. Golbert, p. 188-213, McMillan and Co. Ltd., London, R. Mavrodineanu, ed. (1970).
One major problem with flame photometric analysis is that other elements present in the sample may interfere with the boron spectrum and give erroneous results. It is thus often necessary to separate the boron from the sample prior to analysis. Many boron separation techniques are well known such as electrolysis, chromatography, precipitation, extraction, and distillation. These techniques are often time-consuming and laborious.
Some of these techniques have been used in conjunction with flame photometry. For example, boron may be extracted with methyl isobutyl ketone and the organic solution introduced into a flame, as described by Maeck, et al., Analytical Chemistry, 1963, 35, 63-65. This method is relatively rapid, but it is subject to interferences from ions which are extracted with the boron into the organic phase. Alternatively, it is known that micro amounts of boron can be quantitatively separated from an acid solution by distillation with methanol to form the volatile trimethyl borate ester. The ester may be condensed in a collection flask and analyzed by ordinary means. This method has the disadvantage of requiring distillations of long duration, often on the order of several hours. It may be seen that a need exists for a method of preparing a sample for quantitative determination of boron by flame photometry which is not only easy and rapid but which also minimizes chemical interferences.